Using different size tyres on back and front axles .... is it detramental ??

Hi. I'm running a Discovery 1 ( 1966 ).
I had BF Goodrich AT's all round.
Size of these are 235-70-R16. Due to emergency circumstances, I had to replace the front two tyres with some Pirelli Scorpions, which are a different size of 225-70-R16. I'm out in Bulgaria at present for a couple of months, and at the moment, I can't obtain replacement BFG's due to supply and reasonable price. Will I be able to continue driving on this set up without having any unseen problems, or should I get the same set up back as soon as possible. I don't really want to run different makes of tyres front to back, albeit the same size, as I intend to drive back to the UK in Aug, where Tyres are a lot cheaper, so if I could, I would like to wait till I get back to the UK before I change them again.
Thanks for any help in advance.
Dave

wot ever yu do - dont engage difflock.

No you will damage your centre diff, it will be the same as running different size tyre on the same axle

It appears its only the tyre width that is different 225 as opposed to 235, profile and diameter are the same, so it shouldnt really make any difference.
You should only engage diff lock on slippery surfaces, again, the tyre width wont make any difference as the rolling diameters will be the same in all circumstances.
Allan

its stuck said:

It appears its only the tyre width that is different 225 as opposed to 235, profile and diameter are the same, so it shouldnt really make any difference.
You should only engage diff lock on slippery surfaces, again, the tyre width wont make any difference as the rolling diameters will be the same in all circumstances.
Allan

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Bollixs!
The profile is a % of the width, so if the width changes, so does the diameter for the same profile, so yu will find them (nom) ((235-225)*2*70%) diff in diameter. Having said that, diff tyre manufs do silly things - best to check.
Best option is not to use, or if you must, for the shortest length of time poss. Or remove the front prop.

Should be okay but put the larger tyres on the front axle.

It is not ideal by any means, but most diffs can handle up to a 10% difference and the difference between yours is well within that. I would be pumping up the 225 tyres with a bit higher pressure than normal and the 235 a little less than normal and this should just about eliminate the difference in size. I don't mean by a lot, probably no more than 5 psi each way.

Hi again.
Thanks v. much for all the replies so far. I'm still somewhat in the dark as to how much damage I could possibly do if I continue to drive with this set up, as the replies do seem to conflict slightly. Using a comparison check chart, it's telling me that the overall difference in diameter is 14mm, or -1.9%. Is that a safe difference that I needn't worry about, or should I not drive on them at all ?? I am still looking to change asap, but wouldn't want to risk anything unnecessarily.
Thanks again.

I can't comment on where the other posters get their (contradictory) information from, but I can speak from experience. I've been in a similar situation (different size spare), used a different size tyre temporarily and it didn't damage the car. I'd imagine the people saying "don't do it", haven't done it, so they can't draw on the experience of actually doing it.

I think its one of those "its not to be advised, but shouldnt cause any probs. No guarantees "

Try not to take any notice of the figures printed on the side of the tyre case, when comparing different makes of tyres.

If you had new BFG AT,s on the front with 14mm and old ones on the rear with 4mm then the difference in rolling radius would be greater than percentage difference between the tyre sizes you mention.

My advise would be to check the rolling radius,s yourself.

Put a chalk mark on the tyre where it contacts the road, mark the road, rotate it one full revolution, mark the road again. Do this for the front and rear and measure them.

If you do a percentage calculation, this will tell you the difference. ( you may find that theres very little difference ).

Hope this helps.

Del.

Ok, thanks everybody. I think I'll err on the side of caution at least, and 50 pence's reply made sense with new vs old. I'll check the rolling rad out. Maybe won't be such a big deal after all, plus may have an option from a scrapyard this weekend that I just heard about, so will be going to check it out.
Thanks again all.
Dave

it shouldnt damage the diffs as there open diff and are built to have both wheels spinning at different speeds,it there was a bigger difference it would cause damage over a period of time,just dont engage diff lock as then there is no axial speed difference alowance

i have just spent over 3 hundred...yes three hundred pounds and more on trying to fix my l reg 200 series disco....it gos like this...my tyres were getting a bit lets say on the naughty side so i got a good deal on all five but bigger than what i had on there,money being short i only changed the realy bad ones....the backs so i now had big tyres on the back and smaller ones on the front...then the other night i was driving and bang (from around the gearbox area...then the car was shaking,shuddering pulling to the left and one of the wheels was locking up...i nursed it home at about 2 miles a hour as any faster felt like she was going to break up!!!....i then got a couple of mates around that know about 4x4s well more than me anyway...they test drove it and on inspection both said it was the front axle.....so a week of work and a great big parts list amounting to over 300 quid,and a very oil stained road and pavement outside my house (no drive-way) i was finished i then started the old girl to test my work out to find that the car was no better than what it was when i started the job!!!!!!!!(gutted)......i then took the back prop off and now the car drives without the shuddering and wheel locking up..but the transfer box is clunking and banging (next job) after reading up and a lot of browsing the net i now know that the car is in permenant four wheel drive and not as i thought in two wheel drive,i knew that using the diff lock was out of the question with smaller tyres on the front to the back but as i only used the normal driving range i thought it would be fine...i now have a spare frount axle,diff,hubs,callipers,discs,swivel joints ect.ect.ect and no money left....so if i was you or anyone going to use odd tyres on the two axles i would disconect the back axle untill the tyres are matched again....also put the nuts back on the handbrake hub as it is only held on with one retaining screw!! pack it with washers first the put the nuts back on and the hub will not be overtaking you down the road...i will post again when i have replaced the transfer box....best regards swompy

This makes interesting reading, my first reaction to davety was 'don't worry about it' for the last couple of years I have had 265/75 on the back and 235/85 on the front (on the defender but same difference), I reckoned it gave me most of the benefit of the 265 for towing off road but helped make the steering less vague, I guess I'll go and work out the percentage difference now and have a re-think.

Blanco said:

This makes interesting reading, my first reaction to davety was 'don't worry about it' for the last couple of years I have had 265/75 on the back and 235/85 on the front (on the defender but same difference), I reckoned it gave me most of the benefit of the 265 for towing off road but helped make the steering less vague, I guess I'll go and work out the percentage difference now and have a re-think.

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Your overall tyre diameter should be the same (around 32" it think) so should not cause damage to the diffs

Seem to remember saying (post 3) it was not a good idea as it would damage the centre diff a diff is designed to allow the wheels to travel at different speeds so you can go around corners not so you can run them at different speeds constantly.
This is the problem with part time spanner ****ers who dont actualy know what the **** there talking about, anyone can buy a set of spanners and take things apart even sometimes fix things change a clutch or an axle but when it comes to the more technical parts of a vehicle it should be left to someone who knows what there doing.
There are a lot of people on this site who do know what there talking about but there are a lot who dont.
Some one giving advice on somthing that they dont fully understand to someone who knows even less is going to result an expensive or dangerous **** up.
Sorry rant over.

oldskool said:

Seem to remember saying (post 3) it was not a good idea as it would damage the centre diff a diff is designed to allow the wheels to travel at different speeds so you can go around corners not so you can run them at different speeds constantly.
This is the problem with part time spanner ****ers who dont actualy know what the **** there talking about, anyone can buy a set of spanners and take things apart even sometimes fix things change a clutch or an axle but when it comes to the more technical parts of a vehicle it should be left to someone who knows what there doing.
There are a lot of people on this site who do know what there talking about but there are a lot who dont.
Some one giving advice on somthing that they dont fully understand to someone who knows even less is going to result an expensive or dangerous **** up.
Sorry rant over.

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So what your saying is that you should replace the tyre's on the driven axle/axles at the same time. Because in that case everyone who has a 4X4 needs replace all 4 tyres every time and make sure the spare is the exactly the same tread depth is the same in-case of a puncher. Also he asking about a certain size he is using which is around 7mm different tread depth on a new set, so I don't think it will matter that much hey!!

oldskool said:

This is the problem with part time spanner ****ers who dont actualy know what the **** there talking about, anyone can buy a set of spanners and take things apart even sometimes fix things change a clutch or an axle but when it comes to the more technical parts of a vehicle it should be left to someone who knows what there doing.
There are a lot of people on this site who do know what there talking about but there are a lot who dont.
Some one giving advice on somthing that they dont fully understand to someone who knows even less is going to result an expensive or dangerous **** up.
Sorry rant over.

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I thought a forum was where like minded people could get together and offer advice and help to other members.
So, what youre saying :blabla: is we should just take our cars to the garage because they have proper mechanics and not try to do stuff ourselves?