Bigger tires...go faster?

sharkbait73

New member
This is probably a silly question...but has anyone used larger tires (circumference) to gain a higher top speed at the same rpm for a large truck like a MB 1017, DAF T244, etc?

My understanding is that some of the ex military trucks may max out around 55mph/88km/h. Without changing gearing or rev limiters or anything like that, has anyone tried using larger tires to get 60-65mph (96-105km/h)?

I know it is not much of a change, but around my home, highways are 110km/h. I think I would be comfortable being a 100km/h road block...but 85-88km/h almost seems dangerous, when sometimes it is only single lane each direction.. or even 2-lane but with an endless line of vehicles passing.

Of course room for the tires in the wheel wells (ie. turning, etc) and the power to turn larger tires would also be considerations. Just wondering if anyone has done this?
 

VerMonsterRV

Traveler
Yup, switched ours to 385/65R22.5 tires and gained about 6mph top end. Just Google "tire speed calculator" and you will get a list of sites that will calculate the change in MPH for a change in tire size.
 

Neil

Observer
I have a MB 1017a. I upped the tyes to 385 65x22,5 . Although it must have increased the speed slightly it was hardly noticable, maybe just a few KMPH. This wasnt the reason to change them.

The big change happened when I changed the diffs to a higher ratio. ( Very expensive half the cost of the truck ) The top speed increased by about 25%.

The most important thing though was that it reduced the noise drastically because the revs were lower. Mine sits on the highway at 85kmph at 2000 to 2100 rpm which is very quiet and is good for the engine. It makes the journey so much more comfortable.

If you want a truck that sits at 100 kmph on the highway I wouldnt chose a 1017 as you will be thrashing it .

I did read of the possibility of adding an overdrive unit made by Claas into it but have yet to see one.

The strange thing is that most of us in overland trucks dont want to get to places that fast and are quite happy to sit between 80 to 85 kmph . You see so much more , which is what its all about.

Overlanding is a slow pastime

Neil
 

sharkbait73

New member
Yes it is the "half the cost of the truck" part that made me think (hope) there may be other options. Lol!

Have you ever heard of MB fast axles available separately/surplus (from the "AF" model MBs, I think?). Maybe that would be a cheaper option rather than re-gearing? Or maybe I'm out to lunch lol.

As for the speed expectations, I totally agree in concept...I really enjoy the journey and the actual drive (generally speaking as I don't actually own a future OE vehicle yet).

What concerns me is that when I do need to use highways I don't want to be a hazard to myself or other drivers. Having the ability to drive close to the speed of traffic is important to me in these early years, as I will have to use the highway to access the trips that will be the norm for me early on...until I have the ability to take extended time from work.
 

Neil

Observer
Yes it is the "half the cost of the truck" part that made me think (hope) there may be other options. Lol!

Have you ever heard of MB fast axles available separately/surplus (from the "AF" model MBs, I think?). Maybe that would be a cheaper option rather than re-gearing? Or maybe I'm out to lunch lol.

As for the speed expectations, I totally agree in concept...I really enjoy the journey and the actual drive (generally speaking as I don't actually own a future OE vehicle yet).

What concerns me is that when I do need to use highways I don't want to be a hazard to myself or other drivers. Having the ability to drive close to the speed of traffic is important to me in these early years, as I will have to use the highway to access the trips that will be the norm for me early on...until I have the ability to take extended time from work.
I have never looked at second hand axles. Maybe buying an AF with fast axles os the right way to go. They are however getting rarer and dearer

Neil
 

sharkbait73

New member
I have never looked at second hand axles. Maybe buying an AF with fast axles os the right way to go. They are however getting rarer and dearer

Neil
Yah, I can only imagine. On your 1017...we're the 22.5" rims stock or did you update both tires and rims?

Also, thank you both for your input!

Sent from my Pixel 2 using Tapatalk
 

Sitec

Adventurer
Hi Sharkbait73.
I have a later 1222A and have gone from 10.00 R20" split rims to 315/80 R22.5 tubeless tyres in the hopes that it'd buy me some speed. I found 8 drive tyres on later steel rims which gave me my 2 matching spares. The wheels look a lot better and are ideal for touring as they're interchangeable with 11R's which are readily available if ever needed, but the truck is still only capable of 95kmh just short of the red line (V6 engine). Like you I'm not after speed, but do want to be able to keep with the traffic. I'll have to do something in the not too distant future, just not sure what.

Cheers, Simon.
 

Jostt

Adventurer
I can add to this coments my personal mistake whit the sizes ....because It was Big and expensive, first of all, you must consider which is the initial size , becouse if is 22.5 " rims your truck ,you are límited, second is the power you have to do It, because It is not the same to make longer the ratio by the diferential, or by the tyre...the weiht you add whit a Big tyre afects a lot the riding of the truck, if you have 20 " rims like my case in the unimog , for me 365 80 R20 Will be the máximum tyre size, my truck was fit whit 335 80 R20 as a std, the jump I did was to the 365 85 R20, and whit the short ratios on the axles , It was ok....just 8% more in the top speed, but allways heavy on the stering, at the end I increase 40% betwen overdrive and axles the final ratio to be ok on the highways , 90 km/ at 1900 Rpm, and I come back to small tyres because the Big heavy tyres were to much for the power of my truck, so keep in mind which % you can increase whit the tyres , and which is the target you want to reach, for me no mining whit the tyres if the truck has very low ratios...is just waste money, I have some Donuts in the workshop for sale
 

grizzlyj

Adventurer
You will also be making the brakes less effective with bigger diameter tyres, making the shocks work harder etc.
EU army trucks usually sit at 40mph in convoy, German truck speed limits are I think 40 on most roads as a max unless on motorway. Many trucks of the 1017's era might theoretically max out at 55 but with a load and a slight hill maintaining even 50 might be an issue? With about 200hp (more than standard), bigger but standard option sized tyres, 9500kg (out of I think 11200kg max) and an overcab bed giving some extra wind resistance our U1700 Mog still wouldn't always be able to stay above 50mph on main roads. The Mog/Class overdrive gives you a half lower gear not higher, so other ratios would have to be changed to give higher max speed. Part of our problem was the big jump from 7th to 8th which the Class would have fixed, making it easier to maintain the maximum rather than increasing something we couldn't get to anyway :)
If you think you need to cruise at 60-65 then I would buy a truck designed to do it. People on this forum who have explored North America in a "slow" Euro truck have never said it's an issue that I've read at least.
 

Grenadiers

Adventurer
The Saurer 6dm can easily cruise top speed at 58mph on the highway. However it is quite noisy! We run 14 R20 tires (48" in diameter!), at speed, 2200 rpms. There's no way I'd want to go faster, in fact, we only go this fast on a point A to point B trip, and are not stopping much. The fast axle myth to me, is you're adding a component to a truck that could stress parts up and downstream from the differentials. Much like a Jeep Wrangler outfitted with a Hemi v8 engine, but leaving the Dana 35 rear axle in place. We 'advertise' our highway speed to make people aware of how slow our truck is going. They pause and take pics, so quite a few are not in a hurry to pass~!
 

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Neil

Observer
We changed our wheels and tyres to 385 65 x 22.5 in germany and the vehicle was required to go for a TUV test on the brakes after the change to approve the modification. It was obviously ok.

Here in south america 22.5 inch rims are standard. 20 inch rims are nearly impossible to source. We met a couple who had 4 20 inch tyres shipped from germany. They could not sourcecthem in South America

Dont know about other continents except europe where both are readily available

Availability in the places you intend to go should be a key factor.

22.5 seem to be pretty universal. 20,s are not available in some places

The overall diameter between 385 65 x 22.5 is not much different to 385 20 x 85.

Neil
 

Joe917

Explorer
I can second the fact that 20" tires are not available in South America. 22.5 inch rims also open up a much larger choice of tread patterns.
 

Neil

Observer
Joe. I agree. I can only speak for South America but the last thing you want her is 20 inch rims. You just cant get the tyres. I have heard from other travellers that the same problem exists in Asia and Africa .

Maybe someone could verify this.

Making the correct choice from the outset is critical

Neil
 
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