NSX-R gearing for free (well sort of)

[markc]

I will shortly need new rear tyres for my car (NA2 on 16" front 17" rear) and given the unavailability of OE fit Bridgestones and Dunlops set about looking at alternatives.

OE tyre sizes are 215x45x16 and 245x40x17

I'm currently running on 225x45x16 and 255x40x17 Bridgestone S03 Pole Positions due to an emergency requirement for rear tyres whilst on tour in Italy 2 1/2 years ago. The 255's were all that were available so 225 front were purchased to match when I got home.

While the S03's work well and retain the correct front to rear size ratio to keep the TCS happy, I'm aware that they raise the gearing a touch (by 1.3%) which is not what any NSX needs. As an aside I'm not as keen on the look of the larger tyre (a bit ballon like) so I was looking to return to standard sizes.

Now, the stock NSX uses a 4.06:1 final drive ratio and the NSX-R uses 4.235:1 ie the NSX-R is geared 4.1% lower... bear with me.

Whilst looking for companies who make tyres in these sizes it occurred to me that I could actually lower the gearing by carefull selection of the tyre size. Using an internet tyre size calculator I checked various tyre sizes to see what they did for my gearing.

Here's a list of tyre size, diameter, rolling radius, revolutions per mile, speedometer and odometer differences... (using my factory fit as the baseline)

Front
215/45-16 23.6" 74.2" 854/mi 60MPH 10000mi N/A (STANDARD)

205/50-15 23.1" 72.5" 874/mi 61MPH 10237mi -2.3% (NA1)

205/45-16 23.3" 73.1" 867/mi 61MPH 10152mi -1.5%
225/45-16 24.0" 75.3" 841/mi 59MPH 9852mi 1.5%
215/40-16 22.8" 71.5" 886/mi 62MPH 10372mi -3.6% ***

215/40-17 23.8" 74.7" 848/mi 60MPH 9935mi 0.7% (>2002)
225/40-17 24.1" 75.7" 837/mi 59MPH 9805mi 2.0%
205/40-17 23.5" 73.7" 860/mi 60MPH 10069mi -0.7%
215/35-17 22.9" 72.0" 880/mi 62MPH 10302mi -2.9% ###

Rear
245/40-17 24.7" 77.6" 816/mi 60MPH 10000mi N/A (STANDARD)

225/50-16 24.9" 78.1" 811/mi 60MPH 9943mi 0.6% (NA1)

245/35-17 23.8" 74.6" 849/mi 62MPH 10406mi -3.9% ***
255/40-17 25.0" 78.6" 806/mi 59MPH 9874mi 1.3% (>2002)
255/35-17 24.0" 75.5" 839/mi 62MPH 10287mi -2.8%

245/40-18 25.7" 80.8" 784/mi 58MPH 9611mi 4.0%
245/35-18 24.8" 77.8" 815/mi 60MPH 9986mi 0.1%
255/35-18 25.0" 78.6" 806/mi 59MPH 9876mi 1.3%
265/35-18 25.3" 79.5" 797/mi 59MPH 9768mi 2.4%
245/30-18 23.8" 74.7" 848/mi 62MPH 10391mi -3.8%
255/30-18 24.0" 75.5" 840/mi 62MPH 10288mi -2.8% ###
265/30-18 24.3" 76.2" 831/mi 61MPH 10188mi -1.8%
285/30-18 24.7" 77.7" 815/mi 60MPH 9994mi 0.1%

My personal preference is for the 215x40x16 and 245x35x17 combo giving me 3.9% lower gearing while keeping standard widths and the correct front to rear ratio. Pretty damn close to NSX-R gearing :) So does anyone make a matching set ie both these sizes in the same design???

Turns out Toyo (Proxes T1R) and Falken (FK452) do these sizes. While not Premium brands (or prices) they're certainly tier 2 and are both pretty good bits of kit.

Other observations and concerns...

The original standard wheel/tyre combo for 1990-1994 NA1 and NA1 NSX-R is 0.6% higher geared than 1994-2001 wheel/tyre combo.
The original standard wheel/tyre combo for >2002 cars and NA2 NSX-R is 1.3% higher geared than 1994-2001 wheel/tyre combo.
The 255x35x17 does not seem to exist so is not an option for me or >2002 owners.
My proposed 40 profile front and 35 profile rear lower the car by half an inch (14mm)... which is good.
My proposed 40 profile front and 35 profile rear will not fill the wheelarch as well, from a side on view... which is bad.
The lower overall gearing will improve the acceleration in all gears, especially good for 6th... which is good.
The smaller tyres will be lighter... which is good.
The reduced sidewall height of the lower profiles should make up for the design not having sidewalls as stiff as the OE tyres... which is good.

I know it goes against the conventional grain not to "upgrade" to wider tyres BUT this idea does seem to have some logic. Any comments or corrections to my calculations and observations would be welcome.

Cheers

Mark

[NSXGB]

A small observation would be that you would be putting more miles on your speedo than you actually would be doing.
And an inch and a half is not 14mm. . . :)
From my calcs you would be lowering the car by just over 6mm.
If I remember right the 245x40 tyre dimension means that the height of the sidewalls is determined by the '40' which means it is 40% of the width. Then divide by 2 for either side of the wheel.

Could be wrong though. . .

[forumadmin]

You're nuts. My comments;

It might look silly.

Gearing and acceleration is one small part of driving. How about working out what you gain in a small lowering of gearing, and see what it comes to in terms of acceleration.

When going to large tyres in proper track compounds cornering speeds have gone up more than any perceived loss in acceleration. Indeed with exit speeds being higher, there's not so much need to accelerate anyway.

Braking is better with big sticky tyres.

Low profile tyres feel hard on the road. My track wheels came with 35 profile 285's and they felt nasty.

All my comments relate to the track, which is after all, all I do.

[goldnsx]

You gain a little bit in acceleration but loose a lot of braking and cornering capabilities.

On the German Autobahn I love the 245/40/17 because they accelerate hard but in the mountains I love the 255/40/17 for having more grip. You can feel the difference but I'd never go smaller than 245/40/17 in the rear.

If you really want the 4.23 buy the parts and don't play with the tires. :)

[markc]

And an inch and a half is not 14mm. . . :)
From my calcs you would be lowering the car by just over 6mm.
If I remember right the 245x40 tyre dimension means that the height of the sidewalls is determined by the '40' which means it is 40% of the width. Then divide by 2 for either side of the wheel.

Could be wrong though. . .

14mm is correct but as you say that is not 1.5 inches (I'll amend the post). The car is therefore lowered just over 0.5 inches at the rear. Just under 0.5 inches at the front. Still good :)


You're nuts. My comments;

It might look silly.

Gearing and acceleration is one small part of driving. How about working out what you gain in a small lowering of gearing, and see what it comes to in terms of acceleration.

When going to large tyres in proper track compounds cornering speeds have gone up more than any perceived loss in acceleration. Indeed with exit speeds being higher, there's not so much need to accelerate anyway.

Braking is better with big sticky tyres.

Low profile tyres feel hard on the road. My track wheels came with 35 profile 285's and they felt nasty.

All my comments relate to the track, which is after all, all I do.

You're right about the nuts part :)

My biggest concern is that it'd look silly. Tirerack's "try it on the vehicle" feature won't allow me to do a virtual test fit as it choses tyre size for you.

I'm mainly talking about road driving for the 16/17 combo. Gearing becomes virtually the same as the NA2 NSX-R and most people think it's gearing is best of all the NSX's.
I've no fears over the lower profile ruining the ride, bigger heavier tyres are just as likely to do that.

Braking and grip is primarily about contact patch, combined with tyre stickiness. Contact patch is as much to do with pressure as width but I take your point.

My spare 17/18's will host my trackday tyres. I'd like to go Toyo R888 or Kumho V70 but tyre sizes are limited. I favour the consistency these tyres provide over the extra grip they offer. I'd probably go 205x40x17 front 255x35x18 rear.

Watch this space :)

Mark

[markc]

You gain a little bit in acceleration but loose a lot of braking and cornering capabilities.

On the German Autobahn I love the 245/40/17 because they accelerate hard but in the mountains I love the 255/40/17 for having more grip. You can feel the difference but I'd never go smaller than 245/40/17 in the rear.

If you really want the 4.23 buy the parts and don't play with the tires. :)

Are you using exactly the same tyre ie brand, age, tread depth? I honestly doubt you'd notice any differance in braking and grip with those things being equal and a smidge less pressure in the 245's (probably 1-2 lbs) to make the contact patch the same at the 255's.

Why not buy the 4.23:1 diff?
It's very expensive to buy
It's time consuming (expensive) to fit
It doesn't work with the 6spd g'box (speed sensor issues)

The tyre profile option seemed like logical thing to try or at least discuss... which is what we're doing :)

Cheers

Mark

[goldnsx]

Are you using exactly the same tyre ie brand, age, tread depth? I honestly doubt you'd notice any differance in braking and grip with those things being equal and a smidge less pressure in the 245's (probably 1-2 lbs) to make the contact patch the same at the 255's.

Tyre brand: YES, DON'T MIX tyres on the NSX. ;)
Age: I need a full set every 2 years.

Your argument doesn't hold, means you're comparing apples to oranges. ;) Why lowering the tire pressure of a 245 and keep the one of a 255 high. It's not the width of a tire mainly which increases the contact area but much more the tire diameter and you'd like to go for smaller ones. Imagine driving with bycicle tires on the NSX. Very scary. :cool:

[markc]

Tyre brand: YES, DON'T MIX tyres on the NSX. ;)
Age: I need a full set every 2 years.

So just to be clear, you use the same brand and design of tyre for both your 245x40x17 and 255x40x17 rears and renew them every 2years regardless of wear? Out of interest what brand/design is your preferred tyre?


Your argument doesn't hold, means you're comparing apples to oranges. ;) Why lowering the tire pressure of a 245 and keep the one of a 255 high. It's not the width of a tire mainly which increases the contact area but much more the tire diameter and you'd like to go for smaller ones. Imagine driving with bycicle tires on the NSX. Very scary. :cool:

You make a good point, contact patch is determined by diameter as much as width ie a longer contact patch as well as a wider one, BUT both are effected by pressure. I still think a slightly lower pressure would equalise the contact patch between a 245x40x17 and a 255x40x17.
However, the smaller diameter of my proposed 35 profile 245x35x17 tyre may well result in a noticably smaller (shorter) contact patch and reduce traction & grip. The bicycle tyre analogy is a little exaggerated but makes the point :)

The NSX isn't soo powerful that it seriously troubles the traction made available by the rear tyres, even the original 225x50x16's, so 245x35x17's might work well and also deliver the extra acceleration offered by the lower gearing.

Cheers

Mark

[modarr]

Hey Mark
Don't let the **** grind you down man, just go with it.

I was laughed at by the Track God for running 205 40 17 R888 on the front with 255 18 on the back. Thing is, despite terrible worries about understeer the car is absolutely amazing on track and that includes a very wet Brands Hatch.

So forget the crap about R888's in the wet, contact patches etc, you can drive around the tyre limitations if you know what each end of the car is doing and be plenty quick (as you are).

On the road the acceleration gains with gearing reduction are really barely noticeable. I have the JDM short gears and 2002 R final drive and on the road it makes little difference other than earlier gear changes. On track it makes a small difference, really only a question of being in the power band exiting more corners rather than faster down the straights. The 6 speed box is by far the best option I reckon.

I wouldn't have thought that on road the smaller width rubber would make any difference unless you drive on road like a maniac.

I am all for narrower rubber and nibble handling. I run the supercharged MX5 on 185's and its plenty good.

You'd still be healing and toeing your way round the track on bicycle tyres I reckon.

Mo

[TheQuietOne]

Mo, just a quick note to say how close are you to having the SC installed? It appears you were lucky to tag in on the successful GB before it all went south, and that you got that little beauty over the water safely. Of all the things that have been sent to my factory before going onward that was the coolest box :D

Sorry to crash the thread - I'll mod myself out in time...:rolleyes:

[markc]

I am all for narrower rubber and nibble handling. I run the supercharged MX5 on 185's and its plenty good.

You'd still be healing and toeing your way round the track on bicycle tyres I reckon.

Mo

Hi Mo, good to see you posting :)

When I acquired the 16/17 BBS wheels they came with 205x45x16 and 245x40x17 Bridgestone RE711 tyres (no I've never heard of them before either). I did Silverstone GP circuit with these and the car felt fine. On the road it felt lighter on it's feet ie more nimble compared to the wider SO3PP's I have on now. Whether this was due to the narrower width, the tread design/construction or lighter weight is open to question but I think prefered them.

Unlike you and Kevin I don't have the brakes (yet) to really work sticky track day tyres like R888's, but as I said I'd like the better consistancy they offer over normal road tyres.

I'm hoping to get out on a track day or 2 this year so hopefully I see you out there with one of your supercharged wonders :)

Cheers

Mark

[forumadmin]

The R888s with their stiff sidewalls mean they react much quicker than normal tyres. This was the first thing I noticed about them. The TypeR RE070s are the same. They do work in the wet just fine as well, or rather better than you think they would. I have only used them once in the dry so far, and haven't used them to their fullest either.

Agree with Mo regarding the acceleration due to gearing, and he knows this already as we compared notes one day. Maybe I haven't taken full advantage of the recent changes just yet. This summer will hopefully see me at some tracks again to find out.

[goldnsx]

So just to be clear, you use the same brand and design of tyre for both your 245x40x17 and 255x40x17 rears and renew them every 2years regardless of wear? Out of interest what brand/design is your preferred tyre?

No, it happens that I have to change the rears every year and the front ones every two years. So in the end I'll have a fresh set every two years on the car. ;) The 215/255 is my main set with RE050. The other combo 16/17 with 215 in the rear will only be used on occasions but you're right that I don't have scheme for them.

[modarr]

I'm hoping to get out on a track day or 2 this year so hopefully I see you out there with one of your supercharged wonders :)


Hi Mark
Had a major accident nearly 9 months ago and hence the trackdays are out of the question for a while.

No, my car isn't available for spares so no vultures please.

This was more of a....er .....yet more pattering of small feet type accident.

Hope to be blown by the end of the year and chewing on some GT3 butt.
MO

[Lankstarr]

Mo - good to see you posting mate, but sorry to hear you had a "pattering".

Hopefully you're OK and the reason for not getting back is purely car damage. She'll come back to you and big nastier than ever with her big blower:)

Hope to see you out later in the year.

Luke

[NSXGB]

Mo - good to see you posting mate, but sorry to hear you had a "pattering".

Hopefully you're OK and the reason for not getting back is purely car damage. She'll come back to you and big nastier than ever with her big blower:)

Hope to see you out later in the year.

Luke

Luke, I believe you may have the wrong end of the stick (?), Mo's accident was not in his car...but in his bedroom....:).

[markc]

This was more of a....er .....yet more pattering of small feet type accident.

Congratulations MO :)


Hope to be blown by the end of the year...

You and me both mate but I've already had my birthday this year so Christmas it is ;)


... and chewing on some GT3 butt.MO

The GT3's weren't that much faster than me at Silverstone (GP), I reckon a Racing Brake oversize disc kit and R888's all round will see me worrying all but the fastest GT3's... well 996 GT3's anyway.

Mark

[NSX 2000]

You and me both mate but I've already had my birthday this year so Christmas it is ;)
Mark

LMAO

In fact I'm grinning from ear to ear just thinking about it!

[modarr]

Thanks to all for your concerns and congratulations!

Yes the pattering should really be feet if all goes well.

Mark I would agree, big brakes, R888 and stiff suspension is really all you need. My 3.0 just can't keep up on the long straights and you can't out-brake a GT3 even though I can corner as fast as one in most cases.
As for your Xmas present, how many superchargers do you need?

[TheQuietOne]

LMAO

In fact I'm grinning from ear to ear just thinking about it!

Should we be worried you're grinning thinking of Mark being blown Paul :eek:.

Nice to see some humour back on this forum - I think it has been in recession for too long...:)