Mercedes Sprinter Tyre/Wheel Change

[teemyob]

Hello all,

I have a MB Sprinter running on 6 195/70/15 Tyres. This gives a high Engine revs of 3100rpm @70 Mph. By changing the wheels and tyres to the new MB 235/65/16 this will bring the revs down to a more reasonable 2700rpm.

Does anyone know what kit I would need in order to reprogram the ECU to accept the new tyres?

Trev

 

[jberks]

I would imagine that if this is possible (ECU may not have this pre-programmed in as it wasn't expected at built time) then you would need an MB star tac machine. Dealers or specialists only I suspect.

 

[mister_cee333]

Hi,

The Diff (rear axle) ratio differs from model to model. The ratio is stamped on a plate on the diff (probably covered by a partly stuck sticker).
My 308 is around 3250 revs at 70mph, where if i changed the diff the one fitted to the 311 then it would be around 2800 revs at same speed. I intend to do this when i can source a good one with both driveshafts. (I have previously posted a thread on this - search rear axle changing on sprinter, or this link http://forums.mercedesclub.org.uk/showthread.php?t=21709&highlight=sprinter [if i'm doing the link correctly]).

Regarding changing of wheel and tyre sizes i think you would find that the circumference of your existing wheels would be about the same as the suggested ones and therefore the distance covered by one rotation would not alter and therefore the revs would stay about the same.


Changing the diff would be a fair size job and not to be taken lightly tho.

Hope this helps.

 

[Sprint'n'Go]

Hi, Regarding changing of wheel and tyre sizes i think you would find that the circumference of your existing wheels would be about the same as the suggested ones and therefore the distance covered by one rotation would not alter and therefore the revs would stay about the same.

I think MrC may have his maths wrong?

my reckoning is as follows

15" rim measures 381mm diameter
tyre wall height is 70% of 195mm = 136.5mm

Therefore overall diameter of 195/70/15 is 654mm
which give a theoretical rolling circumference(diameter x Pi) = 2055mm

16" rim = 406.5mm plus 2 x sidewall(65% of 235mm) = diameter of 712mm
theoretical rolling circumference = 2237mm

this nearly a 9% change so Rpm at 70mph should drop to 2825rpm


The problem is which van are you starting with? It sounds as if you have a twin wheeler 4 series Sprinter so changing to single wheels may make your van illegal as the rear tyres will not match the maximium load of the back axle. This WILL invalidate your insurance and also any ministry/VOSA inspectors will spot this straight away at a roadside check. I am not sure if the new 6 bolt wheels will fit onto the old twin wheel axles, I think they are also 6 bolts but may be a different pcd (bolt spacing)

If you have the lighter 2 series sprinter that runs on single wheels at 195/70/15 then you still can't change to the newer wheels as they are 6 bolt fixing instead of the 5 bolts on single wheel old sprinters. However mercedes did give you the option when new, to go for the 3 series wheels (225/70/15) which are taller than the 195's but not quite as big as the 235's on 16" rims.
Be aware that changing to a taller wheel will affect braking performance so you will need to check if the brakes are the same on, say, a 211 as a 311. I have this problem on my land rover and do suffer with more brake fade when running on very tall mud tyres. Again, if it does all fit you will need to tell your insurance.

As far as telling the ECU, I think this will only be neccesary if that is where the speedo signal comes from. I am sure if this is the case then anyone with access to STAR diagnostics should be able to alter the speedo calibration. If this is not the case then you will have to find out how the speedo signal is processed ( I think it may come from the ABS sensors but possibly not as not all sprinters have ABS)

Hope this helps.

Let us know what vehicle you are starting with and how you get on.

 

[teemyob]

Hello,

Thanks for your replies.

I have a 416 Sprinter Motorhome. I think I may just go one size up from 195/70/15 to 205/70/15. This will give me less choice of tyres but will give me stronger ones and around a 2.5% decrease in revs.

Any other suggestions?

Trev

 

[Bolide]

My tyre size calculator lets you compare two sizes

Bolide tyre size calculator
http://www.bolide.co.uk/actions/info.taf?page=tyresizecalculator

Nick Froome
www.w124.co.uk

 

[Sprint'n'Go]

Crikey, That's a long time for a response!

My 316 had the 4.111 axle ratio and 225/70R15 tyres. This gave an almost exact 25mph per 1000 revs so just under 3000rpm at 70mph and a top speed of just over 100mph before hitting the rev limiter (and the electronic speed limiter is set to 100mph unless a lower setting is requested).

To be honest, your ratios aren't giving you much different and you are not really going to gain a noticable benefit from altering the tyres. My van was an 11ft tall luton and it couldn't quite hit 100mph until I got it Superchipped. I would guess your current ratio gives you the best compromise between cruising comfort and the ability to pick up and go when the chips are down. Any movement in either direction may lead to dissapointment in an otherwise well thought out package, Mercedes don't just pick the ratios at random and a motorhome is neither light nor svelte so taller gearing is not advisable.

Now, the fact I had mine superchipped might give you the impression I am a boy racer speed merchant (I can be some days ) but the fact is I often spent an awful lot of time on cruise control at just 65mph for anything upto 500 miles a day and I never found myself wishing for taller gearing to lower the engine revs. On the otherhand I did factory order my van with the 4.111 final drive in place of the 4.375 that comes as standard on the chassis cabs, it always struck me as a bit odd that Merc gave the same gearing package to the 109hp/270Nm package as they did for the 156hp/330Nm 5cyl engine.

It would be interesting to know what final drive ratio you have? I assume you have the 6 speed sprintshift auto box which is popular in motorhomes? the final drive ratio is on the chassis data plate which is in the drivers side footwell and is displayed as i=4.111 if the final drive is 1:4.111.

I wouldn,t recommend changing to wider tyres on a twin wheeler, you need a space between them for good reason. You could however go to a taller tyre of the same width (if one exists) such as a 195/80 or 195/85. Just make sure you maintain or increase the tyre load index to avoid overloading your tyres. A good commercial tyre depot will be able to advise you here but in todays environment you might find many establishments reluctant to supply anything other than the standard replacement.

Let us know how you get on (hopefully in less than 18 months :grin

Steve

 

[teemyob]

Hello, been a while since I had the Idea.

I changed from 195/70/15 to 205/70/15.

Have to say it is one of the best things I ever did. Revs are down from around 2,900 @60 to 2,700 with no noticable downsides. Upside is quieter cab, slightly better fuel consumption, stronger tyres and less sheering of oil.

Highly recomended,
Trev.