Gearing with tires

We run the Escorts with 205/15/50's

The back stretch of Lime Rock is pretty tough with the gearing, we are way out of 3rd and can't do the uphill turn in 4th very well.

I'm wondering if using 13's would make much of a difference? Maybe getting into 4th a bit sooner?

What are the chances then of running out of 4th on the front straight?

We have the "normal" green tag trannies.

ps - I'm speaking for me mostly, Tim has his own driving style, but the last time we ran he found that going back to 3rd at the uphill worked better as well, but they're just pain in the butt shifts.

Thanks,

Diane
1.9L HO, 5 speed

Di--It isn't the wheel diameter, but the overall diameter of the tire and wheel that control "gearing".

You'll have to compare the manufacturers charts, although you may find that a 205 -60X 13 may be closer to a 205-50X 15 than a 225-45 X13.

Heck, you can even go with 14(s).

I worried a bit about this with the dirt stocker 13(s) I have. They are about an inch smaller overall than the normal dry tires. Because they are only usable in deluges, it really did not matter.

Please share your comparison after researching the specs.

Diane,

If you want to calculate your speed in each gear and compare different tire diameters, final drives, etc., then use this formula in an Excel spread sheet:

MPH = (RPM * Tire Diameter(in inches))/(Final Drive * Gear Ration * 336)

My spread sheet shows the speed in 100 rpm increments from 4000RPM to 500rpm over my redline. I only bothered to display 2nd thru 5th gears since I don't use first except for starting.

This way I can decide if I want to risk 'carrying' a gear a little bit longer vs upshifting, only to brake and downshift a second later.

Joe, I am trying *not* to get another wheel size. http://Forums.ImprovedTouring.com/it/tongue.gif But yes, I can use either size and I do understand it's the total diameter that will make a difference. I'll be honest and say I didn't look to see which sizes were available in 13's, it may turn out they are so close to the 15's it doesn't matter.

I also have Dirt Stockers on 13's but I just got them this summer and haven't used them yet. The rain lap times are slow enough so that I don't have that 4th gear problem though. LOL

Greg, thanks for the formula, I'll dig into 13" sizes and crunch some numbers

Still hoping someone out there tried it. http://Forums.ImprovedTouring.com/it/wink.gif


Thanks,

Diane

Diane, I have some 215/50-13 Kumhos you can look at, they're about 21.5" tall compared to 23" for a 205/50-15 tire. This is probably the cheapest tire you can get into that is short enough to make it worthwhile. Hoosier has the 225/45's and 225/50's, and Yoko does a 215/50-13 as well, but they're all $40-60 per tire more expensive.

Bob

Quote:

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Originally posted by Ascona1973:
Diane, I have some 215/50-13 Kumhos you can look at, they're about 21.5" tall compared to 23" for a 205/50-15 tire. This is probably the cheapest tire you can get into that is short enough to make it worthwhile.
<snip>

Bob

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You know, I'm skimming your response and thinking "that's a nice offer but where is this guy?" LOL Teach me not to read screen names first.

Are you offering them for trial use? That may be worth looking into even for a practice session next year, still not sure about our schedule though.

Of course maybe with a freshened motor I'll get into 4th quicker and it will be a non-issue (I can always dream can't I?)

We can chat more later, and I still have to do the spreadsheet work with the gear ratios.

Thanks,

Diane

Dianne,

A short note to remind you that some very light wheels are available in spun steel at various offsets from various outlets. You might consider them to gain additional energy availability from reducing rotating mass. They were listed as mini-stock wheels. We actually bought 13's to get the lighter wheel, and considered the smaller wheel/tire for gearing.

Good racing.

Bill

Quote:

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Originally posted by Diane:
Joe, I am trying *not* to get another wheel size. http://Forums.ImprovedTouring.com/it/tongue.gif But yes, I can use either size and I do understand it's the total diameter that will make a difference. I'll be honest and say I didn't look to see which sizes were available in 13's, it may turn out they are so close to the 15's it doesn't matter.


I also have Dirt Stockers on 13's but I just got them this summer and haven't used them yet. The rain lap times are slow enough so that I don't have that 4th gear problem though. LOL

Greg, thanks for the formula, I'll dig into 13" sizes and crunch some numbers

Still hoping someone out there tried it. http://Forums.ImprovedTouring.com/it/wink.gif


Thanks,

Diane

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I've got a set of 13X61/2 I ran in ITB if you want them $100+whatever freight.



[This message has been edited by stroubelan (edited December 17, 2003).]

Quote:

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Originally posted by stroubelan:

I've got a set of 13X61/2 I ran in ITB if you want them $100+whatever freight.

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I'll send you an email. But 6" is the limit for ITB, as it is the car came with 15x6.5's that I can't run.

I knew I knew your name from somewhere. http://Forums.ImprovedTouring.com/it/wink.gif


Diane