[Tgo]

Some elementary physics applied to the windshield wiper blade does not show promising results for the wiper blade upsizing trend that many of us ponder about.

Take the wiper assembly of any vehicle. The wiper arm has has a spring which pulls the arm against the windshield. The spring is component providing the constant force to the wiper arm.

Lets focus on the pressure. This is a cross section of the edge which equates to a point on the edge. Source

The wiper blade assembly (one which has the rubber edge) is always under this force which is a constant. Lets call it F. The length of the blade is L. Each point on the edge in contact with the windshield has a component of this force which would be the pressure = F / L ( Considering line contact for simplicity).

Elementary Physics applied to a wiper blade.

From common understanding, more pressure helps the edge push more firmly against the windshield, which should equate to better wiping performance.

When we upsize, we are reducing the pressure with which the edge sits against the windshield. Which should result in decreased performance BUT, longer life.

Keeping apples to apples comparison (same style of blade), the only reasons I could come up with for upsizing was the Increased sweep coverage. Is it that important than getting a clean sweep?

So, why do we & why should we, still upsize the wipers?

[GTO]

Thread moved out from the Assembly Line. Thanks for sharing!

I've always stuck to OEM sizes. This seems like a solution to a problem no one had!

[Dr.AD]

Originally Posted by Tgo

When we upsize, we are reducing the pressure with which the edge sits against the windshield. Which should result in decreased performance BUT, longer life.

Keeping apples to apples comparison (same style of blade), the only reasons I could come up with for upsizing was the Increased sweep coverage. Is it that important than getting a clean sweep?

So, why do we & why should we, still upsize the wipers?

I think your analysis is correct. Increasing the wiper blade size will decrease the pressure (Force per unit length in this case of linear contact) and that will reduce the wiping performance, but gain increased sweep area. However, increased sweep area is very tricky, because modern cars have complex windshield shapes, and trying to increase the sweep area may result into interference between the two blades (I have seen this happening on a few cars), and/or the blades touching the outer edge of the windshield and making hitting sounds (I have seen this happening on a few cars too).

There is often not enough room all around the windshield to simply increase the sweep area by using a larger blade and not cause any interference. If that was indeed possible, most car manufacturers would have used a bigger blade in the first place.

Originally Posted by GTO

I've always stuck to OEM sizes. This seems like a solution to a problem no one had!

+1 to this. Well said. Wiper designs are quite complex, and most OEMs do a tight fit based on windshield shapes, sizes, and maximum coverage area possible without any interference. Trying to mess up with that often results into unnecessary problems which did not exist in the first place.

[dhanushs]

Originally Posted by Tgo

...

From common understanding, more pressure helps the edge push more firmly against the windshield, which should equate to better wiping performance....
................................
So, why do we & why should we, still upsize the wipers?

There is a certain amount of pressure which clears off water off the windshield. Once that point is achieved, any more pressure means really nothing.

There is a certain amount of tolerance in the manufacturing of every component in a car, and that is what we take advantage of, while upgrading. Just like we take advantage of the Torque rating tolerances of the gearboxes and driveshafts while remapping, in this case we are taking advantage of the spring stiffness to increase the wiping area.

So, if you can get more wiping area with a larger blade, without interfering with the other blades or windsheild beadings, go for it.

[RedTerrano]

Over the years, I have owned (including family) and driven
Premier Padmini
Maruti 800
Wagon R
Santro
Terrano

I have always been satisfied with the stock wipers. Ok not really. Premier Padmini sucked but thats long gone now.
I change my wipers ever year at the fag end of summer, irrespective of their condition. Also just before the onset of rains (and whenever possible during monsoons) I prefer to apply hydrophobic spray/gel. End result : clear visibility.

[TrackDay]

For most of the cars that I have driven, owned or been driven in, the OEM size blades seems to get the job done pretty well, provided the blades are changed every year. Regarding this aspect of increased length to reduce force on the windshield (and gain life), wont the wiper blades be unsteady at high speeds ?

If there is any place that wipers need an upgrade, it is usually at the rear. Most hatches or SUVs have very small wipers at the rear that cant be upgraded due to the short window height.

[bejoy]

I agree with the analysis. Also the longer size causes more drag - more load on the motor.

I think upsizing was never a requirement, but an outcome of upgrading.

OEM wiper blades are upgraded for better quality of wiping, lesser wiping noise and probably reducing the wind noise (Aero blades?)

Most upgrade paths are towards generic sizes, which though lists the model numbers but slightly vary in their sizes. So if the same length is not available, pick the longer one.

I had better success with a shorter one (Bosch) for the driver side of my Palio (rare blade length). And it lasted many monsoons.

[vrprabhu]

Originally Posted by bejoy

.. Most upgrade paths are towards generic sizes, which though lists the model numbers but slightly vary in their sizes. So if the same length is not available, pick the longer one.

I had better success with a shorter one (Bosch) for the driver side of my Palio (rare blade length)...

Err.. what is the correct size for Palio? I am using 24" (driver side) and 16" (passenger side). Strangely, there is no mention of wiper size in the owner's manual. It the manufacturers who specify the car for which the wipers are suitable. Is this common for all car manufacturers?

BTW, I have used 22" * 18" for my Palio, but didn't notice any significant variation in the wiping pattern, other than the triangular area left out (at the point where the two wipers almost meet when they are at rest). What I have noticed is that, while using the longer ones, during fast (high speed) wiping, the wipers are close to touching one another, leading me to conclude that the longer length reduced the speed of arm travel.

[nkrishnap]

One size upsize generally does not cause much issues. More than the size, the quality of wiper blades matter big time in the quality of wiping. Switch over to better ones, and if you already have a good design, replace them every year to get the optimal cleaning on the windshield.

[Thermodynamics]

Once I changed OEM frame blades and upsized them with Flat / beam blades. There wasn't any reduction in wiping efficiency, in fact it was much better, neat and full.

However it had another problem, during heavy rains when wiping had to be at full speed, the upsized blades flex beyond windshield. This can get very noisy as it bumps with A pillar, wiper gets damaged, paintwork is in trouble. Ocasionally it even gets tangled with things like radio antenna.

IMO, it is better to stick with OEM design or do a thorough homework before upsizing.

[sridhar-v]

it all depends on the condition of your wiper motor and glass surface. Clearance of the sweep area is the other consideration.
I have gone from 19" both sides to a combo of 22" on driver side and 20" on passenger side.

[Amsdoc]

You cant argue with the Physics. But it will remain the same for all cars with all sizes. So if a car has bigger sized OEM blades and you downsize , you will get better force in that blade too. Plus, in my opinion, in the real world the difference in force/pressure is likely to be negligible to make a functional impact. So in the end what matters in optimal sweep area without causing any other issues like banging against the other blade or going out of the glass area.
My Figo wiper blade suddenly split this year. I change them almost every year before the monsoons. But with the lockdown, I could not get a new proper size delivered. I had a spare new set but one which was 1 size up on the drivers side. I have fitted those and whilst it does overlap the passenger side blade a bit, it doesn't bang or go out of the glass area at any point at any speed. The result it better than before, but probably that is to do with a better quality wiper blade. So I don't think it makes a difference going a size up. It is the best sweep area that matters (which I think the OEMs would be tested and decided upon in most cases)

[scorpian]

I have usually upgraded to a inch bigger to get more better clean area and it has never ever had any effect on the cleaning efficiency compared to stock sizes.
Till the time it dosent mess with your other wiper or goes out of the windshield i think its safer and better to upgrade.
Never had any issues and been doing so for last many years. Infact a slightly bigger wiper helps me clean my rear windshield better with a more cleaner and larger view area.

[Brumby]

I always stick to OEM sizes. Any increase in pressure on the glass due to wipers may result in increased probability for developing rubbing marks on the glass.

The cheaper cars have low quality glass which is more prone to such kind of wear.

[a4anurag]

Of the two vehicles at home, the Creta has perfectly sized wiper blades whereas, on the Ertiga, I find them a tad small since there is a considerate amount of gap left during the sweep.

Creta:
Driver side: 26" and Passenger side: 16"



New Ertiga
Driver's side: 22" and Passenger side wiper: 16"


Feel like switching to 24" on the driver side and leave the passenger side as is. Just a thought but not sure how it will work out.