2 birds with 1 stone: lower profile tires to lower & stiffen gearing?

Rick418cars: You are mistaken about the effects on quarter mile time. Trap speed would NOT increase (that's a function of horsepower and weight, and hardly moves at all with gearing), but the effect on quarter mile TIME would be very significant.

More importantly, the biggest benefits would be at low speeds, where the effect on acceleration would be VERY pronounced.

I have done this to other cars and motorcycles, and run a small web-based performance modeling business. I use my own custom software (I am a degreed mechanical engineer with a lot of driveline gearing experience).

I haven't had time to model the SSR yet (fair bit of setup work to feed in all the relevant variables), but here are some examples of regearing efefcts:

1990 Mustang convertible: changed from 2.73 to 3.73 axle. Dropped quarter mile time by 0.70 seconds.

2000 Ducati 996 superbike: dropped quarter mile time by 0.85 seconds.

In both cases, I could have gone further, but the prime objective was NOT best quarter mile time, but rather better street and highway response.

The other advantage of reducing ride height by tire size instead of by springs, is that you do NOT affect the front end geometry AT ALL! The front suspension arms remain in exactly the same position as before the swap. This is a powerful advantage on our SSRs where an aggressive height drop will puit the front end out of its acceptable adjustment range.

IF we can figure out how to make the change in tire size look decent, this approach is VERY effective for ride height and street repsonse both, and is RELATIVELY inexpensive compared to other mods of comparable effect. You need 4 tires (costly ones, admittedly) plus repgramming of the tire size in the ECU (do at dealer or via Predator or Microtuner - they can do that).

Jim G

shorter tires

JimGnitecki said:

We all know that the stock height on the SSR is a bit "high".

Some of us have also figured out that while the 3.73 axle is a step in the right direction, a 4800 lb vehicle like the SSR would feel a LOT betetr with even stiffer gearing. (Yes, really)

If any of you have tried driving around in 3rd versus OD in the 35 to 50 mph range, you will know what I am talking about.

Swapping the rear axle ratio to a 4.11 seems costly. I have gotten 2 quotes, one at $650 but hedging a bit without the quoter at a local hi performance shop doing the detailed parts research, and the second quote at $950, from a different Chevy high performance shop with a strong local reputation, and after the man had done the detailed parts research.

One way of MAYBE killing 2 birds with one stone is to find suitable tires, still with the right load carrying capacity and speed rating and handling characteristics of course, that are lower profile than the stock 295 / 40 x 20 tires.

Those tires are 29.25" in diameter.

IF suitable 295/35 tires exist, they would 28.1 " in diameter, and so would yield a 4% gearing advantage. That's a start! The SSR would e lowered by 0.6 inch.

Even better, would be something like a 290/35, which would give 28.0" diameter, for a 4.5 % gearing advantage, The SSR would be lowered by a tiny bit more than 0.6 inch.

Betetr yet, a 290 / 30 if such a tire exists in the right load rating, as that would give a 26.9" diameter, for a 8.2% gearing improvement! THAT would almost as good as a 4.11 axle ratio. The SSR would be lowered by 1.2 inches.

Anybody out there a tire expert?

Do suitable low profile tires (maybe other than the ones I casually calculated above) exist?

Jim G

Click to expand...

hey JIM, here are a few shorter tire options.. 245X35X19'' =25.75'' front and 285X30X20'' = 26.73'' rear... these wheels companies have a match of tires (HANKOOK VENTUS SPORT K-104)-(FALKEN GRB FK-451)-(DUNLOP SP SPORT 9000) -(BRIDGESTONE POTENZA S-03)-(BRIDGESTONE POTENZA RE050A)-(BF GOODRICH G-FORCE T/A KDW NT) another option for the rear is 295X25x20''=25.80'', (MICHELIN PILOT SPORT A/S and MICHELIN PILOT SPORT PS2) they have a matching front set 245X35X19''=25.75 and (PIRELLI P-ZERO NERO) 305x25x20''=26.00'' but they do not have a match front...........i hope this helps (MOE) :seeya

Thanks, Moe!

You are correct. I checked www.tirerack.com. The load ratings are all enough to meet or exceed what the axles can handle, and the gear ratio increases range from 10% to 14%. The 305 size however will NOT work because it requires a minimum 10.5 inch rim width, per the tire manufacturers' specs. The other sizes are good though.

I need to get a photoshop mockup for appearance. That's going to be, as Rick418cars suggests above, the determinging factor.

I HAVE been able to start modeling in the software tonight. The SSR IS indeed very responsive to gearing changes, because of its high weight. Upping the gearing by 10% reduces 0 to 60 time by 0.36 second. Upping the gearing by 14% reduces 0 to 60 by slightly over half a second! The 14% is achieved via the 295/25 -20 tire size (which as you point out IS available). But, the drop in height is 1 3/4 inches(!!) and the appearance is a key question. hence, the need for a Photoshop mockup.

Jim G