alantr4 Posted March 5, 2008 Report Share Posted March 5, 2008 Anyone out there know roughly which cogs I should be using with 165x15 tyres and a standard ratio diff in my TR4...My halda still has the cogs in from my spitfire days and they wont be any good. I dont have the calibration gears to run a test either.. All help gratefully recieved Alan Quote Link to post Share on other sites
Tr4Tony Posted March 5, 2008 Report Share Posted March 5, 2008 Alan I was running 142 and 27 in BST82B with 175 x 70 x 15 tyres (was the 4.33:1 diff) and have 127 and 22 in 3VC tonight (4.1:1 diff) - both with 22% overdrive - the variation between tyres is usually no more than 1.5% new to worn out, but if the organisers mile is out slightly (which they always are) you really need to calibrate in each time so a decent selection of x gears is needed. Ive got by so far with 22, 27 and 32 y gears. Try 127 and 22 - if its reasonably similar you should be within 5% as were never more than that out each time we run the halda. Better still, buy a Brantz 2 tripmeter as most of the UK rallies will let you run one. Regards Tony Anyone out there know roughly which cogs I should be using with 165x15 tyres and a standard ratio diff in my TR4...My halda still has the cogs in from my spitfire days and they wont be any good. I dont have the calibration gears to run a test either.. All help gratefully recieved Alan Quote Link to post Share on other sites
alantr4 Posted March 5, 2008 Author Report Share Posted March 5, 2008 Alan I was running 142 and 27 in BST82B with 175 x 70 x 15 tyres (was the 4.33:1 diff) and have 127 and 22 in 3VC tonight (4.1:1 diff) - both with 22% overdrive - the variation between tyres is usually no more than 1.5% new to worn out, but if the organisers mile is out slightly (which they always are) you really need to calibrate in each time so a decent selection of x gears is needed. Ive got by so far with 22, 27 and 32 y gears. Try 127 and 22 - if its reasonably similar you should be within 5% as were never more than that out each time we run the halda. Better still, buy a Brantz 2 tripmeter as most of the UK rallies will let you run one. Regards Tony Thanks Tony The infamous Tulip only allows Haldas,ever since someone was caught using a Retrotrip with an average speed computer built into it!!!! looking at the old RAC form I got with the car I think it is fitted with a 3.7 diff..Any ideas what difference that would make??Ive always been hopeless working out anything remotely technical... rgds Alan Quote Link to post Share on other sites
david ferry Posted March 5, 2008 Report Share Posted March 5, 2008 (edited) Alan, Have a go with either the spreadsheet that you can find in the top entry on this google search. Google search I hope! I found this a little while ago and kept it on my laptop. I have yet to use it as the car doesn't yet move under it's own steam! Consequently, I don't know if it works but assume that it does until I find out otherwise. After all, it's only maths! You will need to work out your measured distance accurately with some other method. Or you could use the Autochron version from their website. There is also a suggestion of creating your own measured distances. You'll have to scroll down the website to find the spreadsheet. Autochron Instructions Hopefully, one or other of the spreadsheets will help you work out what X and Z gears you need to change to from whatever you have installed. Good luck Regards David Edited March 5, 2008 by david ferry Quote Link to post Share on other sites
brydon Posted March 5, 2008 Report Share Posted March 5, 2008 Hi Alan I run a '57 TR3 with 3.7 Diff, A type 22% overdrive, 165/15 Michelin XZX on 4.5 60 spoke wires. The above should be a good comparison with a standard TR4. Both my tripmeter & twinmaster run 144/27, and are as Tony says sometimes more accurate than the organiser's Mile Good luck on the rally Kind regards Andrew Quote Link to post Share on other sites
Tr4Tony Posted March 6, 2008 Report Share Posted March 6, 2008 Alan Ive set out a measured mile on the A30 by Blackbushe airport ....shhhhhh. Looks for the yellow and red posts. Its dead straight. Thats where youll see me trucking along in powder blue of a misty night. Best you can do is the spreadsheet calc thing David points you at, but bear in mind the diff ratio and tyre rolling radius. Id say if you take a 22, 27, 32 and 138 to 146 youll get it 100%. Rob and I manage it regularly (although I have a full set of gears) using the same two runs of cogs. Regards Tony Quote Link to post Share on other sites
alantr4 Posted March 6, 2008 Author Report Share Posted March 6, 2008 Hi Alan I run a '57 TR3 with 3.7 Diff, A type 22% overdrive, 165/15 Michelin XZX on 4.5 60 spoke wires. The above should be a good comparison with a standard TR4. Both my tripmeter & twinmaster run 144/27, and are as Tony says sometimes more accurate than the organiser's Mile Good luck on the rally Kind regards Andrew I will try this combo first of all as it sounds like it will be bang on. Thanks a lot Andrew Quote Link to post Share on other sites
alantr4 Posted March 6, 2008 Author Report Share Posted March 6, 2008 Guys Really appreciate your help on this but Ive just realised i will need it to read in kilometers rather than miles!!! ARRRGGHHH ..Maths isnt my strong point so any help gratefully recieved...15 TRs entered on the Tulip now including at least 2 Ex works cars.. I ordered the french Tr book yesterday ... Alan Quote Link to post Share on other sites
brydon Posted March 7, 2008 Report Share Posted March 7, 2008 Alan Using the same conversion table, you require 129/39 for KPH Kind regards Andrew Quote Link to post Share on other sites
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.